The present invention relates to a data transmission in a ring LAN system and more particularly to transmission of system control information in the ring LAN system.
A technique concerning the data transmission in a ring LAN system in which a plurality of data transmission devices are connected in a ring through a transmission path, is disclosed known in Japanese Patent Unexamined Publication No. 61-210742.
In this technique, a data transmission device required to urgently transmit data can preferentially secure a special area of a data transmission area in a transmission frame which circulates the data transmission through the ring LAN system.
In the above technique, however, when one data transmission device uses the special area in a usual operation, another data transmission device can not use the special area.
As a result flexibility in utilization of the data transmission area is diminished and the data transmission area is not utilized efficiently. This causes a problem in that a waiting time from generating the point of a request for transmitting data to ann actual transmission thereof is increased.
Particularly, this problem is significantly important when the number of data transmission devices in the ring LAN system is increased.
Furthermore, when a failure such as disconnection of the transmission path occurs in the ring LAN system and circulation through the transmission frame in the ring LAN system is failed, circulation through the data transmission area in the ring LAN system is also failed, so that the data transmission is failed.
In the above case, a problem that means for transmitting data without use of the data transmission area must be arranged newly in the ring LAN system, thereby complicating the processes.